1. Field of the Invention
The present invention relates to a rotary compressor for driving a refrigeration cycle.
2. Description of the Related Art
The refrigeration cycle in an air conditioning apparatus generally comprises a four-way valve, an indoor heat exchanger, expansion means such as a capillary tube, and an outdoor heat exchanger, all being connected to a rotary compressor of a single cylinder type in this order. A heating or cooling cycle can be attained when the flow passage of the refrigeration cycle is switched by the four-way valve.
Recently, there is provided an air conditioning apparatus of this type wherein a rotary compressor of a capacity-variable type is used so that the capacity of the refrigeration cycle can be varied in response to the loads applied. Generally, this compressor has motor and compressor sections housed in a closed casing, and an inverter circuit is connected to the motor section. The operation frequency for the motor section is changed by the inverter circuit and the number of rotations thereof is thus changed, so that the capacity of the compressor section which is driven by the motor section can be linearly varied.
However, the rotary compressor, whose capacity can be changed by the inverter circuit, has the following problems. As compared with the rotary compressors of the constant rotary type which have no inverter circuit, the rotary compressor with the inverter circuit produces a magnetic sound which is created by the operation of the inverter circuit, and as the capacity of the rotary compressor is enhanced, the number of rotations of the motor section is greatly increased, resulting in increased noise and vibrations. This makes it necessary to improve the quality of those parts which are caused to frictionally contract one another such as the crankshaft and the bearing and to make these parts sound-proof. Thus, the manufacturing cost of the compressor with the inverter circuit is higher than that of the constant rotary type compressor.
In addition, a power loss of more than 10% is caused to occur due to the combination of the inverter circuit and the compressor, as compared to the case wherein no inverter circuit is used. Further, the control section which includes the inverter circuit is also very costly.
Japanese Utility Model disclosure No. 59-123681 discloses a two-cylinder rotary compressor. The capacity of the compressor can be changed, without using the inverter circuit, by selectively stopping the compressing operation of one of the cylinders.
In the case of this compressor, however, its capacity can only be changed at two times; when the compressing operation of one of the cylinders is stopped and when the two cylinders are engaged in the compressing operation. As compared with the case wherein the inverter circuit is used, the capacity of this two-cylinder rotary compressor cannot be minutely changed in response to the loads applied.